Electronic saw-tooth pulse generator



Dec. 21, 1948. a. c. SZIKLAI I ELECTRONIC SAW TOOTH PULSE GENERATOR Filed March 20, 1945 1 Z 7 {ply m Patented Dec. 21, 1948 ELECTRONIC SAW-TOOTH PULSE GENERATOR George C. Sziklai, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 20, 1945, Serial No. 583,801

9 Claims. 1

This invention relates generally to electronic apparatus and more particularly to improved sawtooth pulse generators and electronic switching tube apparatus employed therewith.

The invention relates specifically to saw-tooth pulse generating circuits utilizing novel nonpolarized low impedance electronic switches which are controllable by weak high frequency electrical keying signals. Suchapparatus has particular applications to cathode ray oscillographic and television cathode ray deflection systems.

Conventional saw-tooth pulse generators employing thermionic vacuum tubes require special wave damping circuits since the high resistance of the thormionic vacuum tubes employed as switching devices permit oscillatory currents to circulate throughout the circuit. Such oscillatory currents must be effectively suppressed to provide a substantially linear saw-tooth output voltage wave-form. Also such suppressor circuits and high resistance switching tubes dissipate considerable energy, thereby requiring the use of relatively high power apparatus for providing the required high voltage saw-tooth deflecting pulses.

The instant invention employs novel bidirectional thermionic tubes of the orbital-beam type. Due to the relatively high operating efilciency inherent in such secondary emission tubes, the switching resistance is relatively low, and the bidirectional characteristics of the device eliminate the necessity for oscillatory current suppressor circuits. The measured efiiciency of the instant system is of the order of times that of other known systems, thereby permitting the use of apparatus having relatively low power ratings.

Among the objects of the invention are to provide an improved method of and means for generating saw-tooth pulse electrical currents. Another object is to provide an improved saw-tooth pulse generator employing a novel bidirectional electronic switch. An additional object is to provide a novel pulse generator employing a bidirectional orbital-beam electronic switching device; A further object of the invention is to provide a saw-tooth pulse generator having high operating efliciency characteristics. Another object of the invention is to provide a continuously operating saw-tooth generator utilizing a novel bidirectional electronic switch which eliminates the necessity for oscillatory current suppressor networks.

Other objects of the invention are to provide an improved high voltage undirectional power source. Another object is to provide an improved deflection voltage generator for oscillographic apparatus. An additional object is to provide a novel bidirectional electronic switch. A further object is to provide a novel electronic bidirectional switch utilizing secondary electronic emission for obtaining high operating efliciency. A still further object is to provide an improved bidirection a1 electronic switch of orbital-beam type. Another object is to provide an improved bidirectional electronic switch of cycloidal beam type.

The invention will -be described theoretically and with reference to specific circuits and structure by reference to. the accompanyingdrawlng of which Figure 1 is a schematic circuit diagram for explaining the basic theory of the system, Figure 2 is a schematic circuit diagram of a first embodiment of the invention adaptable, for example, to television kinescope deflection'circuits, Figure 3 is a schematic circuit diagram of a second embodiment of the invention adapted to simultaneous operation for deflection of a television cathode ray beam and for supplying high unidirectional operating voltages for external circuits, Figure 4 is a graph illustrating voltage characteristics in the circuit, Figure 5 is a graph illustrating current characteristics in the circuit, Figure 6 is a schematic circuit diagram of a third embodiment of the invention having similar applications to the circuit of Figure 3 and employing a novel bidirectional electronic switch, Figure '7 is a cross-sectional plan view of a first novel type of bidirectional electronic-switch, Figure 8 is a cross-sectional plan view of a second novel bidirectional electronic switch of orbital-beam type, and Figure 9 is a cross-sectional plan view of a third novel bidrectional switch of cycloidal beam type. Similar reference characters are applied to similar elements throughout the drawing.

Referring to the drawing,'the circuit of Fig. 1 shows the basic circuit of many conventional types of saw-tooth pulse generators. The battery EB represents a power source (which in more detailed circuits may comprise a charged storage capacitor), S represents an ideal bidirectional switch capable of high speed operation and designed to withstand high voltages in its open position andhaving perfect bidirectional conduction in its closed position; L represents an inductive load such, for example, as a deflecting yoke for a television kinescope tube, and C is the distributed capacitance of said yoke. The circuit may be assumed to include no resistance.

When the switch S is first closed at time ii, the

. 3 current (see Figure 5) will increase linearly with time:

until at time t: the switch is opened. Then the current stored in the inductance L will be discharged through the capacitance C in an oscillatory manner, (the solution for. the equilibrium equation being If the switch is closed at time t: corresponding to the end of a half period of the self resonance of the inductor, the inductance returns its energy to the battery Ea with the current changing linearly with time until the instant n, at which time current equilibrium occurs. Then the battery will deliver current in a linear manner to the inductance, and the cycle will be repeated.

It will be seen from the foregoing simple analysis that it there is no resistance in the circuit, and the switch system is perfectly bidirectional, no external energy would be required to provide a continuous saw-tooth current (which would be wattless) and the purely reactive load would behave in the same manner as zero power factor loads behave with sinusoidal currents. This condition is true from the fact that deflection of a cathode ray electron beam, by periodic deflecting voltages or currents, requires no work, the reactance of the reflecting yoke acting merely as a fly-wheel for moving the cathode ray beam bidirectionally.

.Flgure 4 represents the voltage which would appear across the inductance L,

(mag) 4 and it will be observed that the waveform of this voltage is substantially the derivative of the current waveform since the voltage is responsive to the rate of change of current through the inductance L. However, the voltage Er. is much greater than the input voltage En, the value being Since the yoke comprising the inductance necessarily includes resistance, the current into the inductance must satisfy the following:

d Rs-L =E (e) or in the exponential form.

E i=%' l- (7 the fact that conventional electron tubes are not bidirectional, and do not actually conduct until the yoke voltage is discharged to a value below the tube anode supply potential. In the interim, the yoke circuit retains its oscillatory characteristics, thereby providing yoke voltages which are distorted, as indicated by the dashed-line portions of the graph of Fig. 4. The yoke current also is distorted as indicated by the dashed-line portions of the graph of Fig. 5.

Some prior systems have employed diode or triode thermionic tubes connected across the inductive load in order to suppress such undesired oscillatory currents, the suppressor tubes operating as switching devices during the time interval when the thermionic switching tube is not conducting due to reversed potentials on its anode. The instant invention, by employing a truly bidirectional electronic switching device, eliminates the necessity for such oscillatory current suppressor circuits since it approximates the operating characteristics of a perfect bidirectional switch.

Referring to Fig. 2, a bidirectional electronic switch 3 comprises an evacuated envelope containing a thermionic cathode K, a control electrode G1, a pair of secondary-electron-emissive anodes P1 and P2, and a pair of secondary-electron collector electrodes G: and G3, wherein collector electrode G: is responsive to secondary electrons from anode Pi, and collector electrode Gil is responsive to secondary electrons from the anode P2.

A voltage source such as, for example, a battery 5 is connected through a high resistor 1 to charge a storage capacitor 9, one terminal of which is grounded. The charge on the storage capacitor 9 is indicated as Ea. The ungrounded terminal of the storage capacitor 9 is connected to the first anode Pi and to the second collector electrode G: of the bidirectional electronic switch 3. The first collector electrode G2 and the second anode P: are connected to one terminal ll of a reactive load l3 such as, for example, an inductive yoke for deflecting the beam of a cathode ray oscillograph tube. The remaining terminal 15 of the inductive load i3 is grounded. The distributed capacitance of the inductive load 13 is indicated by the capacitance C, shown in dash lilies, connected in shunt with the inductive load. A bias battery I! is connected through a suitable grid resistor between the control electrode G1 and ground to provide fixed operating bias voltages for the control grid, cathode and the second anode. The cathode K is connected to an intermediate point on the bias battery I1. Input signals, having a waveform I9, are applied to the circuit through input terminals 2| connected between the control electrode G1 and ground.

In operation the supply voltage Ea charges the storage capacitor 9 and applies high potential to the first anode P1 and to second collector electrode G3. Positive potential from the bias battery II also is applied to the second anode P2 and the first collector electrode G2. The initial positive pulse portion of the input signal 19 at the time n applied to the control electrode G1, causes primary electrons to pass from the cathode K to both of the secondary-e1ectron-emissive anodes P1 and P2, which each emit relatively large numbers of secondary electrons.

Since the first anode Pi and the second collector electrode G3 are more positive than the second anode P2 and the first collector electrode G2, the secondary electrons emitted from the second anode P: are collected by the second colsame potential.

5 lector electrode Ga, and those emitted from the first anode P1 are returned thereto. This establishes an effective electrical connection between the anodes P1 and P2 causing current to build up in the inductive load I3 according to the law (by assuming no losses in the circuit). This current continues to build up until the time t2, when a relatively high negative pulse is applied to the control electrode G1, thus interrupting the pri mary electrons passing from the cathodes to the anodes P1 and P2. Since no primary electrons reach the anodes, no secondary electrons are emitted therefrom, and the effective circuit between the anodes is opened.

Then the energy stored-up in the inductive load i3 will be discharged by its distributed capacitance C in an oscillatory fashion, as shown in the graph of Fig. 5, between the times t: and ta. At the time t: the control electrode G1 again becomes positive, and primary electrons from the cathode reach the anodes P1 and P2, and again produce secondary-electron-emission therefrom. At this time, the inductive load 13 discharges its energy through the effective connection between 1 the anodes Pi and Pete the storage capacitor 9,

thus returning part of the energy to the power supply during the period between is and t4. At the time t4, both anodes P1 and. P2 are at the At this time, the saw-tooth cycle commencesto repeat, since the first anode P1 becomes more positive than the second anode P2.

Since the potential generated across the inductive load I3 is similar in waveform to that indicated in graph l9 (see Fig. 4), because the input control voltage applied to the input terminals 2| may be derived from a secondary winding coupled to the inductive load I3, as shown and described hereinafter by reference to the circuits of Figs. 3 and 6. Thus, the circuit may be used as a keyed generator or as a continuous generator. depending upon the source of control pulses applied to the control electrode G1.

The bidirectional switching circuit thus described has low series impedance, bidirectional operating characteristics, and because of its high eiliciency requires relatively low cathode emission. The secondary-electron-emissive anodes P1 and P2 may be coated with silver magnesium or other materials which emit secondary electrons of the order of 4 or more times the number of primary electrons impinging thereon. Such surfaces may be operated at high current densities for several thousand hours. Voltage source 5 should preferably be of the order of 200 volts in order to provide ample primary electron emission. Although the anode-to-anode impedance is measurable, the efficiency of the system will be at least 5 times that obtainable when using conventional thermionic switching tubes, since no energy dissipative oscillatory current suppressors are required, and the switch series impedance is substantially reduced.

The circuit of Fig. 3 is similar to the circuit of Fig. 2 except that two conventional orbital beam tubes 23 and 33, each having a control electrode G1. a screen S, a secondary-electron-emissive anode and a secondary-electron collector electrode are substituted for the bidirectional electronic switch 3. Orbital beam tubes of this type are described in an article by H. M. Wagner and W. R. Ferris in the Proceedings of the Institute of-Radio Engineers for November 1941, at pages 598 to 602. Screen voltage for the screen electrodes S is provided by an intermediate connection on a bias battery 13' which is connected between the cathode and the grounded terminal of the reactive load I3. Grid potential for, the control electrodes G1 of the orbital beam tubes 23 and 33 is provided by a second bias battery 21 connected between the cathodes of the tubes and one terminal of a voltage pickup winding 29 which is inductively coupled to the reactive load l3. The remaining terminal of the voltage pickup winding. 29 is connected to the control electrodes G1 of the tubes. Thus, keying voltages of. the type shown in the solid line graph of Fig. 4 are applied to key the control electrodes G1 of the two single orbital beam tubes in the manner described heretofore by reference to the circuit of Fig. 2.

The circuit also may be employed to provide high unidirectional operating voltages for external circuits. A second voltage pickup winding 3|,

simultaneously with the application of saw-tooth deflecting currents to the inductive yoke I3.

A current meter 45 serially connected between the ungrounded terminal of the storage capacitor 9 and the anode and collector electrodes of the orbital beam tubes shows that the current load on the battery source 5 is reduced by a factor of 4 when both orbital beam tubes 23 and 33 are operated simultaneously, as compared with the operation of the circuit when either one of the tubes is operated alone. Thus, the bidirect'lonal operation of the circuit materially \lmproves the circuit efficiency as well as the linearity of the saw-tooth deflecting currents applied to the reactive yoke l3.

The circuit of Figure 6 is similar to the circuit of Fig. 3 with the exception that applicant's novel bidirectional orbital beam tube is substituted for the pair of unidirectional orbital beam tubes 23, 33. The operation of the saw-tooth voltage generator portion of the circuit is identical to that described heretofore by reference to the circuit of Figure 2, except that the control-grid voltage pulses are derived from a voltage pickup winding 29 coupled to the reactive yoke 13, in the same manner as described by reference to the circuit of Figure 3. The high voltage pickup winding 3| also coupled to the reactive yoke 43 provides rectified and filtered unidirectional potential for an external load 43 in the manner previously described.

Figure 7 shows a first embodiment of a bidirectional orbital beam electronic tube which may be employed in the circuits of Figures 2 and 6. An evacuated envelope 46 contains a centrally-disposed cathode K which is surrounded by successive concentrically'disposed control electrodes G1. semi-circular secondary-electron-collector electrodes G2 and G3 disposed on diametrically opposite sides of the cathode K, and diametrically disposed, semi-circular secondary-electron-emissive anodes P1 and P2. Internal or external connections may be rovided between the anode P1 and collector electrode G: and between the anode P: and the collector electrode G2. The operation of the device is as described heretofore by reference to the circuit of Figure 2. One disadvantage of the structure disclosed is that foreign matter emitted by the cathode K directly impinges upon the anodes P1 and P2, thereby causing contamination of the secondary-electron-emissive coatings thereon. Also the collector electrodes G: and G: are subjected to undesirable primaryeiectron emission.

The structure illustrated in Figure 8 is superior to that shown in Figure '1 since primary electrons, emitted by the cathode K and controlled by the surrounding control electrode G1, traverse orbital paths between the cathode and the anodes P1 and P: due to the lens action of a pair of reflector electrodes l1, 9, which are biased negatively with respect to the cathode potential. Primary electrons traversing the orbital paths to the two secondary-electron emissive anodes P1 and P2 do not impinge upon the collector electrodes Ga and G: located adjacent to the anodes P1 and P2, respectively.

Also foreign matter emitted by the cathode is shielded from the anodes by means of the reflector electrode 41 interposed therebetween. Secondary electrons emitted by the anodes P1 and P2. in response to primary electrons impinging thereon, are collected by the adjacently disposed collector electrodes G1 and G3, respectively. Thus, the dual orbital paths provided by the unique reilector electrode construction shown in Figure 8 provides an exceedingly eflicient and stable bidirectional electronic device when the tube is employed in circuits such as those shown in Figures 2 and 6.

A third type of tube construction illustrated in Figure 9 includes a centrally disposed cathode surrounded by a control grid G1 having shielding portions 51 and 53 for preventing direct emission from-the cathode to the flat, edgewise-disposed anodes P1 and P2. A pair of flat reflector electrodes R1 and R2, disposed parallel to and on opposite sides of the anodes P1 and P2, cause the primary electrons emitted by the cathode K to traverse cycloidal paths to the secondary-electron-emissive anodes P1 and P2, both of which emit secondary electrons from both sides faces. The secondary electrons emitted by the anodes P1 and P: are collected by the collector electrodes 01 and G3, respectively adjacent thereto, while the primary electron emission is effectively shielded from the collector electrodes by the cycloidal electron paths provided by the reflector electrodes. Appropriate operating potential polarities are indicated on the anode, collector, and reflector electrodes.

Thus, the invention described comprises several embodiments of novel saw-tooth generator circuits including provisions for obtaining high unilateral operating potential for external circuits. Also three proposed types of bidirectional electronic switching tubes are disclosed and the operation thereof is explained by reference to their use in the disclosed circuits.

. I claim as my invention:

1. A saw-tooth pulse generator including a storage capacitor, a source of unilateral potential, means connecting said source to said capacitor to charge said capacitor, selectively bidirectional thermionic tube means, a reactive load, means connecting said capacitor to said tube means for selectively discharging said capacitor through said 8 tube means and said load. means connecting said load to said tube means for alternately discharging said load through said tube means and said capacitor, and means for keying said tube means to eflect alternate discharges of energy from said capacitor and said load.

2. A saw-tooth pulse generator including a storage capacitor, a source of unilateral potential, means connecting said source to said capacitor to charge said capacitor, bidirectional thermionic tube means comprising at least a cathode. a control electrode, a pair of secondary-electron-emissive anodes and a pair of seccndaz"y-electron-collector electrodes, each of said collector electrodes being responsive to secondary electrons derived substantially only from an adjacent one of said anodes, a reactive load, means connecting said capacitor to said tube means for selectively discharging said capacitor through said tube means and said load, means connecting said load to said tube means for alternately discharging said load through said tube means and said capacitor, a source of keying pulses, and means for applying said keying pulses to said control electrode to eifect alternate discharges of energy from said capacitor and said load.

3. A saw-tooth pulse generator including a storage capacitor, :1 unipotential source, means connecting said source to said capacitor to charge said capacitor, thermionic tube means comprising at least a cathode, a control electrode, a pair of secondary-electron-emissive anodes and a pair of secondary-electron-collector electrodes, each of said collector electrodes being responsive to secondary electrons derived substantially only from an adjacent one of said anodes, a reactive load, means connecting said capacitor to one of said anodes and to the one of said collectors adjacent to the other of said anodes for selectively discharging said capacitor through said one collector, said anodes and said load, means connecting said load to the other of said anodes and the other of said collectors adjacent said one of said anodes for alternately discharging said load through said other collector, said anodes and said storage capacitor, a source of keying pulses, and means for applying said keying pulses to said control electrode to effect alternate discharges of energy from said capacitor and said load.

4. A saw-tooth pulse generator including a storage capacitor, a source of unilateral potential, resistive means connecting said source to said capacitor to charge said capacitor, thermionic tube means comprising at least a cathode, a con.

'- trol electrode, a pair of secondary-electron-emissive anodes and a pair of secondary-electron-collector electrodes, each of said collector electrodes being responsive to secondary electrons derived substantially only from an adjacent one of said anodes, a reactive load, means connecting said capacitor to one of said anodes and to the one oi said collectors adjacent to the other of said anodes for discharging said capacitor through said one collector, said anodes and said load, means connecting said load to the other of said anodes and the other of said collectors adjacent said one of said anodes for discharging said load through said other collector, said anodes and said storage capacitor, a source of keying pulses responsive to the rate of change of energy in said load, and means for applying said keying pulses to said control electrode to effect alternate discharges of en ergy from said capacitor and said load.

5. A saw-tooth pulse generator including a storage capacitor, a source of unilateral potential. rel

electrode, a pair of secondary-electron-emissive,

anodes and a pair of secondary-electron-colleclor electrodes, each of said collector electrodes being responsive to secondary electrons derived substantially only from an adjacent one 01' said anodes, a reactive load. means connecting said capacitor to one of said anodes and to the one of said collectors adjacent to the other of said anodes for discharging said capacitor through said tube means and said load, means connecting said load to the other of said anodes and the other of said collectors adjacent said one or said anodes for discharging said load through said tube means and said storage capacitor, a source of keying pulses comprising means reactively coupled to said load, and means for applying said keying pulses to said control electrode to eflect alternate discharges of energy from said capacitor and load.

6. A saw-tooth pulse generator including a storage capacitor, a source of unilateral potential. resistive means connecting said source to said capacitor to charge said capacitor, thermionic tube means comprising at least a cathode, a control electrode, a pair of secondary-electron-emissive anodes and a pair of secondary-electroncollector electrodes, each of said collector electrodes being responsive to secondary electrons derived substantially only from an adjacent one of said anodes, a reactive load, means connecting said capacitor to one of said anodes and to the one of said collectors adjacent to the other of said anodes for discharging said capacitor through said tube means to said'load, means connecting said load to the other of said anodes and the other of said collectors adjacent said one of said anodes for discharging said load through said tube means to said storage capacitor, means reactively coupled to said load providing a source of keying pulses responsive to the rate of change of energy in said load, and means for applying said keying pulses to said control electrode to eilect alternate discharges of energy from said capacitor and said load.

7. A high voltage system including a. storage capacitor, a relatively low voltage source, means connecting said source to said capacitor to charge said capacitor, thermionic tube means comprising at least a cathode, a control electrode, a pair of secondary-electron-emissive anodes and a pair of secondary-electron-collector electrodes. each of said collector electrodes being responsive to sec ondary electrons derived substantially only from an adjacent one of said anodes, a step-up transformer having primary and secondary windings. said primary winding having substantial distributed capacitance, a discharge path for said capacitor including means connecting said capacitor to one oi said anodes and to the one of said collectors adjacent to the other of said anodes for discharging said capacitor through said tube means and said transformer primary winding, a-second discharge path ior the capacitance of said transiormer primary winding including means connecting said primary winding to the other of said anodes and the other of said collectors adjacent said one of said anodes for discharging said transformer primary winding ca-' pacitauee throush said tube means and said capacitor, a source of keying pulses, means for applying said keying pulses to said control electrode to effect alternate discharges of energy irom said said v 10 capacitor and said transformer primary winding capacitance, and means for deriving high alternating potentials from said transformer.

8. A high voltage unipotential system including a storage capacitor, a relatively low voltage unipotential source, means connecting said low voltage source to said capacitor to charge said capacitor, thermionic tube means comprising at least a cathode, a control electrode, a pair of sec ondary-electron-emissive anodes anda pair of secondary-electron-collector electrodes, each of said collector electrodes being responsive to secondary electrons derived substantially only from an adjacent one of said anodes, a transformer having primary and secondary windings, a discharge path for said capacitor including means connecting said capacitor to one of said anode; and to the one of said collectors adjacent to the other of said anodes for discharging said capacitor through said tube means and said transformer primary winding, a second discharge path for the capacitance of said transformer primary winding including means connecting said transformer primary winding to the other of said anodes and the other of said collectors adjacent said one of said anodes for discharging said transformer primary winding through said tube means and said capacitor, means including said transformer comprising a source of keying pulses, means for applying said keying pulses to said control electrode to effect alternate discharges oi. energy from said capacitor and said trans: former, a rectifier responsive to high alternating potentials derived from said transformer, and means for deriving a high D. C. voltage for said rectifier.

9. A saw-tooth pulse generator including a storage capacitor, a source of unilateral potential. means connecting said source to said capacitor to charge said capacitor, selectively bidirect'onal thermionic tube means including at least one secondary-electron-emissive anode and at least one secondary-electron-collector electrode.

a reactive load, means connecting said capacitor to said tube means for selectively discharging said capacitor through said tube means and said load, means connecting said load to said tube .means for alternately discharging said load through said tube means and said capacitor, and

means for keying said tube means to effect alternate discharges of energy from said capacitor and said load, at least alternate ones of said energy discharges being between said secondaryeiectron-emissive anode and collector electrodes.

.g GEORGE C. SZIKLAI.

REFERENCES CITED The following references are of record in the ills of this patent:

UNITED STATES PATENTS 

